This invention is directed to a method for melt spinning from inelastic materials extruded lengths of predetermined cross-sections from predetermined arrangements in spinnerets of non-round orifices of one or no axis of symmetry in the plane of the spinneret face, and to such orifice arrangements in spinnerets for practice of the method by which non-axisymmetric emergence behavior, i.e. "kneeing", of inelastic fluid streams from spinnerets is utilized.
The elimination of nonaxisymmetric emergence behavior of fluid streams i.e., "kneeing" in melt spinning filaments is desirable in a number of instances, and the patents to Paliyenko et, U.S. Pat. Nos. 3,640,670 and 3,734,993; and to Shemdin, U.S. Pat. No. 3,738,789 are concerned with solutions for minimizing or eliminating kneeing of filaments upon extrusion of the filaments from spinnerets.
In a co-filed, co-pending patent application the invention concerns a solution for kneeing of filaments from spinning orifices of non-round cross-section, the orifices having either one or no axis of symmetry in the plane of the spinneret face. The spinning holes or orifices are so formed as to eliminate non-axisymmetric emergence behavior in the spinning of inelastic materials, i.e. to eliminate "kneeing" of filaments as they are extruded from the spinning orifices. In the co-pending invention, each orifice is so dimensioned that the coordinates of the centroid of the square of the velocity profile of the extruding material in the plane perpendicular to the axis of the orifice and the coordinates of the centroid of the velocity profile of the extruding material in the plane perpendicular to the axis of the orifice are essentially coincident at the orifice exit. Such orifice cross-sections are thus essentially non-kneeing. The expression, "essentially non-kneeing" will be explained in more detail herein.
As explained in the co-pending application, a filament "knees" when the line of flow of the extruded filament from the orifice is bent out of the vertical back toward the spinneret face at an angle relative to the perpendicular to the spinneret face. In some instances the filament is bent to such extent that the filament forming material bends back and touches the spinneret face. This leaves a drip or blob of material on the spinneret face which can sometimes block a spinning orifice and interfere with filament formation. Sometimes such "kneeing" undesirably results in the coalescence of two or more adjacent filaments.
An example of a non-round cross-sectioned spinning orifice having one axis of symmetry in the plane of the spinneret face would be a T-shaped cross-section with the leg of the T being perpendicular to the bar of the T and intersecting the bar at its midpoint. A bisector extending through the bar and leg would form two symmetrical halves with the "bisector" constituting the "axis" of the one axis of symmetry. In this example, there are no other possible axes of symmetry in the plane of the spinneret face.
An example of a non-round cross-sectioned orifice having no axis of symmetry in the plane of the spinneret face would be a polygonal configuration having more than four sides, each side of the polygon intersecting at right angles with an adjacent side.
It should be understood that in each of the above examples the spinning orifice has the same shape or configuration throughout its capillary length, and is dimensionally constant or the same throughout the length of the capillary.
Textile yarn filaments having non-round cross-sections have been found to be desirable because different physical and aesthetic properties can be obtained by design, more so than with filaments having round cross-sections.
One example of a non-round cross-section would be an H shaped filament, which can be made from an H shaped spinning orifice. The formation of an H shaped spinning orifice in a spinneret, however, is complex and thus the manufacture of such spinnerets is difficult and costly.
There are various other non-round cross-sections, of course, one of them most frequently in use being a T shaped cross-section. For instance the two Paliyenko et al. patents, U.S. Pat. Nos. 3,640,670 and 3,734,993, mentioned above disclose what is called a "split T" orifice, which is constructed by forming two rectangular orifices spaced from but in close proximity to each other to form a T configuration. One of the rectangular orifices, the "stem", depends perpendicularly from the midpoint of the other rectangular orifice, the "cross-bar". The stem is spaced from the cross to form a gap therebetween of about 0.0001 inch to about 0.008 inch, or preferably about 0.002 inch. Filament forming streams extruding from the split T orifice are said by the patentees "to coalesce in a zone about 1/64 to 1/2 inch from the face of the spinneret plate to form a relatively well defined T-shaped filament". The extrusion from the split T, according to the patentees, occurs "without kneeing". The resulting coalescense is due to the "Barus effect", meaning that the spacing of the two rectangles making up the split T is such as to enable the extruded materials to expand at the exit and thus come into contact with each other. The more elastic the material being extruded, the easier it is to utilize the Barus effect to cause coalescence because of the greater expansion of the material at the exit of the orifice. The construction, however, of a split T is expensive and requires close manufacturing control as the two rectangular orifices making up the T must be spaced very closely but yet not so close as to break through the bridging constituting the space between the two orifices. There is no kneeing from rectangular orifices, each of which has more than one axis of symmetry in the plane of the spinneret face.
There are, however, some instances where nonaxisymmetric emergence behavior of fluid streams, i.e. "kneeing" of the filaments upon emerging from the spinning orifices, are desirable. The instant invention is directed to particular applications of these instances.